The present invention relates to a vehicle occupant protection system and, more particularly, to a system and method for controlling one or more actuatable occupant protection devices, including an actuatable headrest restraint.
Actuatable occupant restraint systems, such as air bags, for vehicles are well known in the art. Such restraint systems include one or more collision sensing devices for sensing vehicle crash acceleration. Air bag restraint systems further include an electrically actuatable igniter, referred to as a squib. When the collision sensing device senses a deployment crash event, an electrical current of sufficient magnitude and duration is passed through the squib to ignite the squib. When ignited, the squib initiates the flow of inflation fluid into an air bag from a source of inflation fluid, as is known in the art.
Certain known collision sensing devices used in actuatable occupant restraint systems are mechanical in nature. Still other known actuatable occupant restraint systems for vehicles include an electrical transducer, such as an accelerometer, for sensing vehicle crash acceleration. A system using an accelerometer as a crash or collision sensor further includes some circuitry, e.g., a controller, for monitoring the output of the accelerometer. The accelerometer provides a signal having an electrical characteristic indicative of the vehicle""s crash acceleration. The accelerometer is operatively connected to a controller, such as a microcomputer, which performs a crash algorithm on the acceleration signal for the purpose of discriminating between a deployment and a non-deployment crash event. When a deployment crash event is determined to be occurring, the restraint device is actuated, e.g., an air bag is deployed.
Many types of crash algorithms for discriminating between deployment and non-deployment crash events are known in the art. Algorithms typically are adapted to detect particular types of crash events for particular vehicle platforms. One example of such an algorithm is taught in U.S. Pat. No. 5,587,906. Other examples of systems for discriminating vehicle crash events are disclosed in U.S. Pat. Nos. 5,935,182 and U.S. Pat. No. 5,758,899.
Air bag restraint systems are also known to require more than one sensor for detection of a deployment crash event. Often, the plural sensors are arranged in a voting scheme in which all the sensors must xe2x80x9cagreexe2x80x9d that a deployment crash event is occurring before restraint actuation is initiated. In certain known arrangements having a first and second sensor, the second sensor is referred to as a xe2x80x9csafing sensor.xe2x80x9d Air bag actuation occurs only if the first sensor and the safing sensor indicate a deployment crash event is occurring.
One aspect of the present invention provides a system for controlling an actuatable occupant protection device. The system includes an actuatable headrest device which, when actuated, helps protect an occupant of a vehicle seat. A crash sensor is operative to sense a condition of the vehicle and provide a crash sensor signal having an electrical characteristic indicative of the sensed vehicle condition. A controller is coupled to the actuatable headrest device and the crash sensor. The controller determines a crash velocity value and a crash displacement value based on the crash sensor signal. The controller has a threshold value functionally related to the determined crash displacement value. The controller controls actuation of the actuatable headrest device in response to the determined crash velocity value relative to the threshold value.
Another aspect of the present invention provides a method for helping protect a vehicle occupant during a vehicle crash event. The method includes sensing vehicle acceleration and determining a crash velocity value based on the sensed acceleration. A crash displacement value is determined as a function of the sensed acceleration. A threshold is provided having a value functionally related to determined crash displacement. Actuation of an actuatable headrest device is controlled in response to the determined crash velocity value relative to the value of the threshold.